1. Technical Field
The present disclosure is directed to a signal conversion system and associated methods for converting a digital input signal to a pulse width modulated output signal and, more particularly, to a signal conversion system with a pulse width modulator. The present disclosure is also directed to a pulse width modulator for use in an audio processing and/or reproduction system. The disclosure is further directed to a low cost, high quality audio encoding, playback and/or streaming process, system, and method.
2. Background
Mobile technologies and consumer electronic devices (CED) continue to expand in use and scope throughout the world. In parallel with continued proliferation, there has been rapid technical advance of device hardware and components, leading to increased computing power and incorporation of new peripherals onboard a device along with reductions in device size, power consumption, etc.
Such devices must routinely handle a range of signal types (e.g. audio signals, video signals, sensory data, etc.), often arising from a variety of sources. Such devices may also routinely generate signals to drive a range of transducer types (e.g. loudspeakers, tactile feedback displays, data communication channel, charge storage elements, display elements, etc.) and/or associated drivers. Many such transducers and/or drivers may be efficiently operated by pulse based driving schemes. In order to manage the interconnection of this wide range of signal types and driving schemes, it is common for such systems to implement sample rate converters and/or pulse width modulators to convert from a first signal to an alternative, pulse based signal. Sample rate conversion aspects may be used to lower computational signal processing requirements, synchronize signal sampling with a system clock, operate with a minimum sample rate, convert to a known sample rate, etc.
Furthermore, the input signals are typically provided from different sources having their own reference clock that differs in frequency, or operates asynchronously from available system clocks. Even though the variation in frequency may be small, due to stability requirements and performance demands in many applications, the data streams must still be sample rate converted in order to maintain synchronization and signal integrity over long sample streams. Use of an intermediate sample rate may also eliminate problems with switching synchronization of signal sources. For example, when a signal processing system is synchronized to an input sample stream (rather than with an independent or stabilized clock) and the sample stream clock changes, fluctuates, or is removed, “glitches” in generated resampled signals can occur.
In the conversion from a resampled signal to a pulse width modulated signal, intermodulation distortion (IMD), total harmonic distortion (THD), and modulation index (MI) based issues may serve to limit quality of the output signal.
Such issues as described above are of particular relevance to the areas of audio processing, video processing and telemetry applications.